<template>
  <div class="upload-excel">
    <el-button
      type="primary"
      size="mini"
      :loading="loading"
      @click="handleUpload"
    >点击上传
    </el-button>

    <input
      ref="excel-upload-input"
      class="excel-upload-input"
      type="file"
      accept=".xlsx, .xls"
      @change="handleClick"
    >

  </div>
</template>

<script>
  // import * as XLSX from 'xlsx'

  export default {
    props: {
      beforeUpload: Function, // eslint-disable-line
      onSuccess: Function // eslint-disable-line
    },
    data() {
      return {
        //遮罩层
        loading: false,
        excelData: {
          header: null,
          results: null
        }
      }
    },
    methods: {
      generateData({header, results}) {
        this.excelData.header = header;
        this.excelData.results = results;
        this.onSuccess && this.onSuccess(this.excelData)
      },
      handleDrop(e) {
        e.stopPropagation();
        e.preventDefault();
        if (this.loading) return;
        const files = e.dataTransfer.files;
        if (files.length !== 1) {
          this.$message.error('Only support uploading one file!');
          return
        }
        const rawFile = files[0];// only use files[0]
        if (!this.isExcel(rawFile)) {
          this.$message.error(
              'Only supports upload .xlsx, .xls, .csv suffix files'
          );
          return false
        }
        this.upload(rawFile);
        e.stopPropagation();
        e.preventDefault()
      },
      handleDragover(e) {
        e.stopPropagation();
        e.preventDefault();
        e.dataTransfer.dropEffect = 'copy'
      },
      /**
       * 触发隐藏域的点击事件
       */
      handleUpload() {
        this.$refs['excel-upload-input'].click()
      },
      /**
       * 文件选择的点击回调
       */
      handleClick(e) {
        const files = e.target.files;
        const rawFile = files[0]; // only use files[0]
        if (!rawFile) return;
        this.upload(rawFile)
      },
      upload(rawFile) {
        this.$refs['excel-upload-input'].value = null; // fix can't select the same excel
        if (!this.beforeUpload) {
          this.readerData(rawFile);
          return
        }
        const before = this.beforeUpload(rawFile);
        if (before) {
          this.readerData(rawFile)
        }
      },
      readerData(rawFile) {
        this.loading = true;
        return new Promise((resolve, reject) => {
          const reader = new FileReader();
          reader.onload = (e) => {
            const data = e.target.result;
            const workbook = XLSX.read(data, {type: 'array'});
            const firstSheetName = workbook.SheetNames[0];
            const worksheet = workbook.Sheets[firstSheetName];
            const header = this.getHeaderRow(worksheet);
            const results = XLSX.utils.sheet_to_json(worksheet);
            this.generateData({header, results});
            this.loading = false;
            resolve()
          };
          reader.readAsArrayBuffer(rawFile)
        })
      },
      getHeaderRow(sheet) {
        const headers = [];
        const range = XLSX.utils.decode_range(sheet['!ref']);
        let C;
        const R = range.s.r;
        for (C = range.s.c; C <= range.e.c; ++C) {
          const cell = sheet[XLSX.utils.encode_cell({c: C, r: R})];
          let hdr = 'UNKNOWN ' + C;
          if (cell && cell.t) hdr = XLSX.utils.format_cell(cell);
          headers.push(hdr)
        }
        return headers
      },
      isExcel(file) {
        return /\.(xlsx|xls|csv)$/.test(file.name)
      }
    }
  }
</script>

<style scoped lang="scss">
  .excel-upload-input {
    display: none;
    z-index: -9999;
  }
</style>
